So far, a material for a printed circuit board for a plastic package or a material for a printed circuit board for a card is required to meet the three conditions shown below.
First, to have excellent flame retardance without addition of a halogen-based compound as a flame retardant, which possibly forms a compound such as polybrominated dibenzodioxin and furan having particularly strong toxicity.
Secondly, to have excellent heat resistance without generation of delamination at a temperature where lead free solder is treated, which is higher than a temperature where conventional solder comprising lead is treated by about 10 to 20° C.
Third, to have high thermal stiffness as a countermeasure for decrease of the warp of a printed circuit board due to higher temperature from use of a lead free solder than the conventional reflow temperature.
With respect to these requirements, a method is suggested, in which 110 parts or more by mass of an inorganic filler is added with respect to 100 parts by mass of an epoxy resin composition, which uses a pre-reacted epoxy resin as a base obtained by reacting a bifunctional epoxy resin and a phosphorus-containing bifunctional phenol in advance, whereby to obtain flame retardance without containing a halogen-based compound and excellent heat resistance, and to improve the thermal stiffness (for example, see Patent Document 1).
However, it is pointed out that with the method mentioned above, large variation of a hole position at the time of process occurs, and it is difficult to balance excellent hole position accuracy and excellent heat resistance, and thermal stiffness, with respect to a drill process for a small drill diameter of 0.20 mm or less associated with further higher density of a printed circuit board in recent years.